The research being proposed involves the use of a film-balance as a model system coupled with electron spin resonance, nuclear magnetic resonance, differential scanning calorimetry and fluorescence studies. Among the problems to be investigated are: 1) The problem of lateral diffusion and segregation in metastable films under well-defined physical conditions. The approach to be taken will include a newly devised monolayer kinetic method and a direct study of the diffusion of fluorescent probes. 2) The difficulties created in interpretation of ESR and fluorescence spectra obtained from spin-label and fluorescent probes in a membrane-like environment. Pure and mixed film studies will be carried out to establish how such molecules may perturb their own environment and what conformations are permitted under given conditions. The role that the precise location of the spin-label or fluorescing group in the probe molecule may play, will also be investigated. 3) The behavior of oxidized forms of cholesterol in model membranes appears to be similar, but not identical, to that of cholesterol itself. This tentative conclusion will be further verified and their possible role in cell lysis examined. 4) Lipid-protein interactions will be investigated using a surface viscometer. A particular emphasis will be placed in the effects the addition of a given protein has on the lipid gel-liquid crystalline transition. The results will be interpreted in terms of previously obtained differential scanning calorimetry data.